Help with heating a gas sensor testing chamber?

[Inquirer3]

Hello,
I am working on an aluminum gas sensor testing chamber, where I will need to apply up to 400 degree C to the sensor being tested. I am wondering what must be done to be able to control the temperature. The created the chamber and left an open area for insulation and nichrome wire connection. How would I be able to control the temperature while also insulating the heat from traveling to the rest of the chamber. The chamber is about 5" x 3" x 3" and the area that the sensor will be placed is only 1 in^2.
Thanks.

 

[Inquirer3]

Response from MrAl:

"...how critical is it that the heat from the inner box does not reach the outer box? I ask because there is no way to create heat inside a small box that is totally enclosed and not have it escape to a larger box that this smaller box is inside unless it is for a limited time duration or there is a port to allow some of the heat to escape the entire enclosure to the outside of the larger box. The physics of nature does not allow that.
To make up for that, you either have to limit the time of the experiment or provide a port that can be used to cool the outside of the smaller box so that the heat from inside can not reach the outside and thus the larger chamber.
There are ways that can improve the workings but in order to know what works and what doesnt there has to be some specification on how much heat could be tolerated in the larger chamber that comes from the smaller chamber. For example styrofoam insulation isnt too bad, but a vacuum sealed enclosure is even better...which do you need...or can you provide a small port and a secondary small box to house the smaller box (3 boxes in total then)."

 

[Inquirer3]

The chamber is designed to withstand high temperatures, and therefore the outer box does not need to remain at room temperature. The target gas is inserted in one end and goes out the other end. I had been planning on applying all heat to the platform in which the sensor will be placed using a nichrome wire and thermocouple for temperature monitoring and control. The chamber is hooked up to a computer program which sends a signal to the sensor. I want to use the same program to deliver varying current (and therefore temperature) to the nichrome wire.
I have no experience with heaters, so I guess I am wondering what the best method for delivering heat will be. Can it be done with a micro-USB?

 

[MrAl]

Hi,

Well it is unclear what you are using for the heater (nichrome wire in a coil perhaps) and ambient temperature.
Also, will the tests be continuous or intermittent, thus giving more time for everything to come back to room temperature.

Heating problems can often be estimated by using electronic circuits with resistors and capacitors. I would hope you have some exposure in this area. The heater would be a voltage or current source for example, and the inner box a capacitor, and the link from inner box to outer box another resistor where the outer box is another capacitor, and the link between outer box and ambient another resistor and the ambient would be a sink. So what we end up with is a low pass filter where each stage node is a temperature. The inner box capacitor voltage represents the temperature of the inner box, the outer box cap voltage represents the outer box temperature. The capacitor values are based on the specific heat capacity of each box, the resistor values are based on the thermal resistance of each box. So the inner box heats up, some heat conducts through the walls to the outer box, then some heat conducts through the walls of that box to the ambient, and the ambient is considered constant temperature.

Does this view make sense to you? Granted it may take some measurements to get the parameters estimated.